1. Field of the Invention
The present invention relates to a filter to be installed in a liquid flow path, a liquid discharge head utilizing such filter, and a producing method therefor.
2. Related Background Art
With the recent advancement in the scientific technologies and image drawing technologies, demand is increasing for a precise filtration of chemical solutions. Particularly in an ink jet printer for forming an image by discharging an ink onto a recording medium, a finer ink droplet is considered essential for attaining a required finer definition in the image. In the recent commercial ink jet printers, the mounted ink jet head generally has a nozzle diameter of 30 μm or less regardless of the ink discharging mechanism, and such nozzle diameter is anticipated to continue to become finer for meeting the requirement for a finer definition in the image. In case of a precise ink discharge from such small nozzle, a foreign matter eventually present in the ink may cause a fluctuation in the volume of the flying ink droplet, thereby deteriorating the precision of image drawing. Also such foreign matter, if deposited around the discharge port, will cause a continuous influence on the precision of discharge. For the purpose of avoiding such phenomenon, a filter for precise filtration is provided in an ink passage in the proximity of the recording head.
A filter used for such purpose has been made by a mesh woven with resinous fibers or metal fibers, or a thin metal plate having apertures formed by a pattern etching or a pattern plating. Also a filter apparatus, utilizing an electrolytic polishing to such metal filter to remove scratches or irregularities on the aperture-containing surface and oxides sticking to the surface thereby preventing agglomeration of the pigment of the ink on such surface, is disclosed for example in Japanese Patent Application Laid-open No. 2001-253083. In such ink jet printer utilizing a pigment, since the image recording is executed by a pigment deposition onto a recording medium, a discharge nozzle has a diameter as large as about 30 μm in comparison with an ink-jet printer utilizing an organic dye. Therefore the former may utilize a coarser filter in comparison with the latter, but it involves a restriction that a filter having fine apertures not passable by the pigment particles cannot be used.
On the other hand, the ink jet printer utilizing a dye as colorant is not associated with the aforementioned restriction for pigment and can utilize a filter with a very small aperture size, such as a sintered non-woven cloth of metal fibers, in order to improve the precision of filtration. It is thus rendered possible to reduce the discharge nozzle to a diameter of about 15 mm for improving the precision of ink discharge and thus improving the image quality. Such sintered non-woven metal fiber cloth for precision filtration is formed by sintering web-shaped stainless steel fibers in a vacuum oven and surface flattening under a press, and is employed in an ink jet printer requiring a high-quality image recording. Also for attaining a filtration of a high precision, there is employed also a filter formed by sandwiching a web-shaped sheet with an average wire diameter of about 5 mm between web-shaped sheets with an average wire diameter of about 15 mm and, after a sintering in a vacuum oven, flattening the surface under a press.
However, in such sintered non-woven metal fiber cloth, as described in Japanese Patent Application Laid-open No. H6-200456, foreign substances of a particle size of about 10 μm, resulting from a sintering spacer used at the sintering operation, may be deposited on the surface of the sintered non-woven metal fiber cloth. Also in the pressing operation executed for surface flattening after the sintering of the metal fiber web, a contaminant may be pressed into the surface of the sintered non-woven metal fiber cloth or may cause a defect or a distortion in the metal fibers.
Also in case of using a sintered non-woven metal fiber cloth with such deposits as a filter, the deposit liberated from the filter may clog the flow path or may be deposited around the port of the discharge nozzle in a recording head with a smaller diameter, and such phenomena result in a loss in the image quality.
Such problems are not limited to the filter installed in the ink jet apparatus as explained above, but are also present in biotechnology- or scientific technology-related apparatuses, in which even a very slight contamination must be prevented and thus require an ultra fine filtration.